The conventional formulation for plumbing solder is 50% by weight of tin and lead. This formulation has a low melting point, wets well, forms a high strength bond with copper pipe, and is easy to apply. The use of lead in solders for potable water plumbing applications has recently become the subject of regulation and legislation in many countries, however, because of toxicological concerns. Several solder producers have responded by attempting to formulate a plumbing solder that melts at a low temperature, sets up quickly, is inexpensive and strong, and otherwise exhibits the excellent physical and mechanical properties of tin/lead solder.
The conventional approach to non-leaded plumbing solders is a tin/antimony composition in the range of approximately 95% tin and 5% antimony by weight ("95/5" solders). Although such solders exhibit adequate strength and hardness properties, they have not been well received by plumbers, mainly because of their extremely high melting point. They are also unsuitable for environments which encounter high cyclic stress and vibration, such as in refrigeration applications. Solders containing approximately 95% tin and 5% silver are frequently substituted in such applications where a non-leaded solder is required.
A number of solders reflect added silver and other metals to the tin/antimony alloy in an effort to lower the melting point, improve flowability and enhance the solder properties. Solders formed of tin, antimony, zinc and silver, for instance, are disclosed in U.S. Pat. No. 4,670,212 issued June 2, 1987. U.S. Pat. No. 4,758,407 issued July 19, 1988 and U.S. Pat. No. 4,695,428 issued Sept. 22, 1987 discuss adding copper to the tin/antimony/zinc/silver composition in order to lend extra body to the solder. Although zinc lowers the melting temperature, it can subject such solders to porosity defects and inconsistencies. U.S. Pat. No. 4,806,309 issued Feb. 21, 1989 discloses a solder containing tin, antimony, bismuth and silver to overcome this problem. The silver is said to compensate for the decreased shear and tensile strength imparted by the bismuth, which lowers the melting temperature of the solder.
A non-tin/antimony approach to non-leaded solders is the tin/copper/silver solder reflected in U.S. Pat. No. 4,778,733 issued Oct. 18, 1988. That patent discloses ternary solders that contain approximately 92-99% by weight of tin, 0.7-6% copper and 0.05-3% silver. The high melting point and broad range between solidus and liquidus phases, however, render such solders more troublesome to apply and slower to set up in use.